Brucellosis, or infection with bacteria from the Brucella genus, is probably one of the most important, widespread, and slightly scary infections that no one has ever heard of. It affects pretty much every mammal (animals with hair and milk) and has probably played at least a minor role in human history. So, what the heck is it?
There are several different species of Brucella bacteria, typically named for the main species of animal that they infect, creativity not being a prime consideration in becoming a bacteriologist. (B. suis is in pigs, B. canis is in dogs, etc.) If the full list is interesting to you, you can find it on the Center for Disease Control (CDC) website for veterinarians, https://www.cdc.gov/brucellosis/veterinarians/host-animals.html. If you followed that link, you may have found that the species that infects cattle is not “bovis” or “beef-us” or something, but B. abortus.
Although it wasn’t discovered first, B. abortus was the first Brucella bacterium named for David Bruce, a British physician who discovered what would be later called B. mellitensis in British soldiers in Malta. He didn’t name it after himself though; the name was changed later in his honor, as was the whole Brucella genus. As you might guess from the name, one of the main symptoms of Brucella infection (henceforth referred to as “Brucellosis”) is abortion. In Veterinary Medicine, we use the term “abortion” mostly to refer to what in human medicine is called “miscarriage,” i.e. the unintentional loss of a pregnancy. In females, Brucellosis will generally also cause loss of fertility, still-birth, and sometimes mastitis, which is infection and inflammation of the mammary glands. The general symptoms in males are also related to loss of fertility, typically via orchitis, or inflammation of the testicles. (interestingly, at least to me, this inflammation can lead the immune system to make antibodies against sperm, which as you can imagine makes things a bit rough when we are trying to keep animals around as breeding stock.) In addition to the reproductive effects, the bacteria can get pretty much anywhere, and so other organ infection can occur.
In animals, the main mode of transmission is either sexual contact (it is, in fact, an animal STI and should be tested for in at-risk animals before breeding), or exposure to placenta or aborted fetuses. The specifics will vary from species to species, but that’s the general idea.
And all of that is well and good, but has little to do with zoonotic disease, which is what I thought we were here to discuss. So, let’s discuss. In humans, the symptoms tend to be… (checking CDC website) …the same basic symptoms of any generalized infection: fever, aches, etc. It does throw in a couple fun ones, such as endocarditis (heart), orchitis (testicles again), as well liver or spleen involvement, etc. My favorite part is the fact that many times the fever will go up and down, which when I learned about it in vet school was referred to as “Undulant Fever.” (Undulating meaning going back and forth. Now that I think about it, wasn’t “Undulant Fever” something from the Disco era?) I misheard it, thought the professor said “Ungulant Fever” and thought, “What a weird way to name that. I know that a lot are from ungulates (hooved mammals), but why would you call it that?” I didn’t realize my mistake (or that I was saying it wrong) until I was studying for the final exam. Oops. Now they seem to call it “recurrent fevers” which avoids the confusion, but lacks a certain… I don’t know what.
Infection in people tends to come from 2 places. The first is workplace exposure, so people raising livestock, working at slaughterhouses, and most relevant to ME, veterinarians. Given the small animal focus of the patients I see, I mostly just have to worry about the occasional dog with orchitis, but large animal veterinarians have to be careful with livestock having reproductive issues, as it is a serious issue. Some types (including in dogs) are reportable diseases, meaning that if we are worried that we might be seeing a case of it, we must contact health authorities to help prevent human illness.
The second, and overall most serious route for exposure is in dairy products. The bacteria routinely end up in the milk of infected animals, so consuming unpasteurized dairy products is a fantastic way to get this disease. The reason that all milk sold in stores MUST be pasteurized is for food safety, largely due to Brucellosis. There are cases in the United States every year in children whose parents went to great lengths to get UN-pasteurized milk for some imagined health benefit. Instead of whatever benefit they thought they would confer on their progeny, instead they just gave them a pretty rough disease that can cause life-long issues.
[Interesting side note, apparently this is not a new problem. Archeologists found evidence of Brucella bacteria in cheese found in a 3,000-year-old Egyptian tomb. It is unlikely to still be infectious, but I don’t think I’d want to eat it anyway…]
The World Health Organization (WHO) recommends that all dairy be pasteurized and that disease in cattle, goats, and sheep specifically be reduced/eradicated through vaccination if common or testing and culling infected herds if uncommon. (If a disease is uncommon in a population, vaccinating all animals can be less effective than testing at achieving eradication in limited areas. Vaccines are still the single most effective method of disease control known, except maybe not defecating in your drinking water.)
The bottom line is that pregnant women for sure, and the rest of us for mostly sure, should really only be eating and drinking pasteurized dairy products. It has turned Brucellosis from a common childhood disease to a rare one, and we really want to keep it that way. There is no health benefit to “raw” milk, and even if it tastes better, it isn’t worth it. And a quick reminder for those of us working in animal-related (or laboratory) fields: wear gloves and keep stuff out of your mouth!